1. Field of the Invention
The present invention relates to an engine air-fuel ratio control method with a venturi type fuel supply device and a fuel control appliance including the method.
2. Prior Art
An air-fuel ratio control method with a venturi type fuel supply device and a fuel control appliance including the method are well known art. For example, the Japanese Application Patent Laid-open Publication No. 2000-18100 discloses a gas fuel engine with a venturi type fuel supply device comprising a venturi chamber located in the upstream of a throttle valve and a passage for supplying fuel into the venturi chamber, wherein CNG (compressed natural gas) is used as the gas fuel. This fuel supply device comprises a 3-port solenoid valve provided on the venturi chamber side in the passage for supplying fuel, a bypass passage connecting the 3-port solenoid valve and an intake system in the downstream of the throttle valve of the engine, and a control means for switching the 3-port solenoid valve at the time of starting of the engine so as to let the gas fuel into the bypass passage. Thereby it aims to improve the startability of the engine, in particular, the startability under low temperature.
Furthermore, the fuel supply device is also provided with a sub-injector in the intake system in the downstream of the throttle valve of the engine, and at the time of acceleration of the engine, the sub-injector is turned on so as to correct the supply quantity of the gas fuel, thereby keeps the operating condition of the engine favorable.